US4609535A - Extracting soluble phosphates from naturally occurring iron and aluminium phosphates using solutions of alkali metal carbonates and hydroxides - Google Patents

Extracting soluble phosphates from naturally occurring iron and aluminium phosphates using solutions of alkali metal carbonates and hydroxides Download PDF

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US4609535A
US4609535A US06/636,601 US63660184A US4609535A US 4609535 A US4609535 A US 4609535A US 63660184 A US63660184 A US 63660184A US 4609535 A US4609535 A US 4609535A
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phosphates
alkali metal
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leachate
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Griffith Thomas
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/30—Alkali metal phosphates
    • C01B25/305—Preparation from phosphorus-containing compounds by alkaline treatment
    • C01B25/306—Preparation from phosphorus-containing compounds by alkaline treatment from phosphates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/01—Treating phosphate ores or other raw phosphate materials to obtain phosphorus or phosphorus compounds

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  • This invention relates to the extraction of soluble phosphates from naturally occurring iron and aluminium phosphates.
  • the present invention is characterised by the use of alkali metal carbonate solutions to leach naturally occurring phosphates.
  • the carbonate leach is followed by further leaching with alkali metal hydroxide.
  • the process of the invention may be applied to many types of naturally occurring phosphates, including those from Christmas Island, Senegal, Brazil and other sources.
  • the carbonate leach is preferably carried out at elevated temperature, for example from 70° C. and the boiling point at atmospheric pressure, or under imposed pressure from 100° to 150° C.
  • barrandite a naturally occurring iron and aluminium phosphate
  • barrandite is leached under pressure at 100°-150° C. with potassium carbonate solution to form a solution of potassium orthophosphate and potassium aluminate.
  • the residual solids are leached further with potassium hydroxide solution at 70°-90° C. to give essentially complete extraction of phosphorus and aluminium in the original barrandite.
  • Residual solids are separated from the solutions and the solutions cooled to separate out potassium orthophosphates.
  • the remaining solution is cooled to precipitate aluminium trihydrate and the resulting potassium carbonate recycled to leach more barrandite.
  • Christmas Island G grade rock a naturally occurring complex calcium iron aluminium phosphate is leached with hot sodium carbonate solution to form a solution of sodium orthophosphates and sodium aluminate.
  • the residual solids are leached with hot sodium hydroxide solution to bring essentially all the phosphorus and aluminium associated with the iron and aluminium in the original rock into solution.
  • Residual solids essentially calcium phosphate and iron hydroxide are separated from the solution which is then cooled to crystallize out sodium orthophosphates.
  • the remaining solution is carbonated to precipitate aluminium hydroxide and the resulting sodium carbonate solution recycled to leach more Christmas Island C grade rock.
  • a calcium phosphate rock contaminated with minor amounts of iron and aluminium phosphates which make it undesirable for conventional fertilizer manufacture is treated to reduce the iron and aluminium content.
  • Low-grade Florida rock is a rock of this type. After leaching with hot sodium carbonate solution, the resulting sodium carbonate and phosphate solution is separated from the unreacted rock and iron hydroxide. The insoluble material is classified to remove as much colloidal iron hydroxide as possible and it is then suitable for conventional fertilizer manufacture.
  • the solution of sodium phosphate and sodium aluminate is cooled to crystallize out sodium orthophosphates and the remaining solution carbonated to produce sodium carbonate and aluminium hydroxide.
  • the sodium carbonate is recycled to leach more low grade Florida rock.
  • My process has the advantage that capital and operating cost of the large decomposers, evaporators and seed recycle equipment is eliminated.
  • the relatively small amount of alkali metal carbonate produced in decomposing the alkali metal aluminate is recycled to dissolve more phosphate rock by reactions 1 and 2.
  • My process has the additional advantage that potassium carbonates and hydroxide can be used to produce valuable potassium phosphate. If potassium hydroxide is used to dissolve iron and aluminium phosphates the resulting potassium aluminate is not suitable for recovery of potassium hydroxide by a process analagous to the Bayer process with sodium aluminate, but potassium aluminate can be readily decomposed by carbon dioxide.
  • the ground barrandite slurry was further reacted with sodium hydroxide in agitated vessels.
  • This sodium hydroxide was added as a 50% solution and the barrandite suspension agitated for 30 minutes at 80° C.
  • the amount of sodium hydroxide added was calculated to be stoichiometrically equivalent to the "caustic available" phosphate present in the original barrandite.
  • "Caustic available” phosphate is defined as total phosphorous less 0.5 times the calcium present e.g. roughly equivalent to calcium phosphate.
  • Residual solids consisting largely of insoluble iron compounds and calcium phosphate, were filtered from the leach solution at 70° C. This clarified solution was then cooled to 20° C. when practically all the phosphate present crystallized as sodium orthophosphates.
  • the sodium orthophosphates were filtered off and the residual sodium aluminate solution reheated to 35° C. and a small amount of aluminium hydroxide added to promote subsequent precipitation. Carbon dioxide was bubbled into the solution to suspend the aluminium hydroxide and decompose the sodium aluminate to sodium carbonate and aluminium hydroxide. After three hours carbonation the aluminium hydroxide was filtered off at 35° C. and the resulting sodium carbonate solution cooled to 20° C. to crystallize out and recover sodium carbonate. The residual solution containing sodium carbonate and a small amount of sodium phosphate was recycled for leaching more barrandite.
  • Example 2 In this experiment the same technique was used as in Example 1 except that after grinding and leaching in recycled sodium carbonate, the ground barrandite slurry was heated to boiling point to drive off some of the carbon dioxide present as sodium bicarbonate. By this means the amount of sodium hydroxide used for subsequent leaching was reduced to 90% of stoichiometric.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Environmental & Geological Engineering (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Geology (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
  • Fertilizers (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Coloring Foods And Improving Nutritive Qualities (AREA)

Abstract

A process for production of alkali metal phosphates from material containing iron and aluminium phosphates comprises leaching the said material with alkali metal carbonate solution to produce a leachate containing dissolved phosphates, and recovering alkali metal phosphates from the leachate. In a preferred embodiment, the carbonate leach is followed by further leaching wth alkali metal hydroxide to effect further dissolution of phosphates from the material, before recovering alkali metal phosphates from the leachate.

Description

This invention relates to the extraction of soluble phosphates from naturally occurring iron and aluminium phosphates.
Previous art involves dissolving complex iron and aluminium phosphates in sodium hydroxide, as will be discussed in more detail below.
The present invention is characterised by the use of alkali metal carbonate solutions to leach naturally occurring phosphates. In a preferred embodiment of the invention the carbonate leach is followed by further leaching with alkali metal hydroxide. The process of the invention may be applied to many types of naturally occurring phosphates, including those from Christmas Island, Senegal, Brazil and other sources.
The carbonate leach is preferably carried out at elevated temperature, for example from 70° C. and the boiling point at atmospheric pressure, or under imposed pressure from 100° to 150° C.
In one form of the invention, barrandite, a naturally occurring iron and aluminium phosphate, is leached under pressure at 100°-150° C. with potassium carbonate solution to form a solution of potassium orthophosphate and potassium aluminate. The residual solids are leached further with potassium hydroxide solution at 70°-90° C. to give essentially complete extraction of phosphorus and aluminium in the original barrandite. Residual solids are separated from the solutions and the solutions cooled to separate out potassium orthophosphates. The remaining solution is cooled to precipitate aluminium trihydrate and the resulting potassium carbonate recycled to leach more barrandite.
In a simplified form the reactions taking place are believed to be:
2FePO.sub.4 +3K.sub.2 CO.sub.3 +3H.sub.2 O→2Fe(OH).sub.3 +2K.sub.3 PO.sub.4 +3CO.sub.2                                       1.
2AlPO.sub.4 +4K.sub.2 CO.sub.3 →2KAlO.sub.2 +2K.sub.3 PO.sub.4 +4CO.sub.2                                                2.
FePO.sub.4 +3KOH→Fe(OH).sub.3 +K.sub.3 PO.sub.4     3.
AlPO.sub.4 +4KOH→KAlO.sub.2 +K.sub.3 PO.sub.4 +2H.sub.2 O 4.
2KAlO.sub.2 +3H.sub.2 O+CO.sub.2 →K.sub.2 CO.sub.3 +2Al(OH).sub.3 5.
In another form of the invention Christmas Island G grade rock, a naturally occurring complex calcium iron aluminium phosphate is leached with hot sodium carbonate solution to form a solution of sodium orthophosphates and sodium aluminate. The residual solids are leached with hot sodium hydroxide solution to bring essentially all the phosphorus and aluminium associated with the iron and aluminium in the original rock into solution. Residual solids essentially calcium phosphate and iron hydroxide are separated from the solution which is then cooled to crystallize out sodium orthophosphates. The remaining solution is carbonated to precipitate aluminium hydroxide and the resulting sodium carbonate solution recycled to leach more Christmas Island C grade rock.
In a simplified form the reactions taking place are believed to be:
2FePO.sub.4 +3Na.sub.2 CO.sub.3 +3H.sub.2 O→2Fe(OH).sub.3 +2Na.sub.3 PO.sub.4 +3CO.sub.2
2AlPO.sub.4 +4Na.sub.2 CO.sub.3 →2NaAlO.sub.2 +Na.sub.3 PO.sub.4 +4CO.sub.2
FePO.sub.4 +3NaOH→Fe(OH).sub.3 +2Na.sub.3 PO.sub.4
AlPO.sub.4 +4NaOH→NaAlO.sub.2 +Na.sub.3 PO.sub.4 +2H.sub.2 O
2NaAlO.sub.2 +CO.sub.2 +3H.sub.2 O→Na.sub.2 CO.sub.3 +2Al(OH).sub.3
In a third form of the invention, a calcium phosphate rock contaminated with minor amounts of iron and aluminium phosphates which make it undesirable for conventional fertilizer manufacture, is treated to reduce the iron and aluminium content. Low-grade Florida rock is a rock of this type. After leaching with hot sodium carbonate solution, the resulting sodium carbonate and phosphate solution is separated from the unreacted rock and iron hydroxide. The insoluble material is classified to remove as much colloidal iron hydroxide as possible and it is then suitable for conventional fertilizer manufacture.
The solution of sodium phosphate and sodium aluminate is cooled to crystallize out sodium orthophosphates and the remaining solution carbonated to produce sodium carbonate and aluminium hydroxide. The sodium carbonate is recycled to leach more low grade Florida rock.
In a simplified form the reactions taking place are believed to be represented by the equations outlined for the second form of the invention.
In the above description of the invention it should be clearly understood that where potassium compounds are mentioned sodium compounds are also applicable and vice versa.
ADVANTAGES
Previous art involves dissolving complex iron and aluminium phosphates in sodium hydroxide. The resulting solution is freed from residual solids, cooled to crystallize out sodium phosphate, and the resulting sodium aluminate solution decomposed into aluminium hydroxide and sodium hydroxide, see Rothbaum and Reeve, "Recovery of Alumina and Phosphate from Christmas Island C Phosphate" N. Z. Journal of Science Vol. II No. 4, December, 1968.
This technique has the apparent advantage that the sodium associated with aluminium in solution can be recovered as sodium hydroxide. However the decomposition of sodium aluminate, the Bayer process, requires large decomposition vessels, the recirculation of large volumes of seed aluminium hydroxide and the use of relatively dilute solutions to promote the decomposition of sodium aluminate. The recovered sodium hydroxide solution from Bayer decomposition
NaAlO.sub.2 +2H.sub.2 O⃡NaOH+Al(OH).sub.3
has to be evaporated for reuse. It will be observed from equation 2 that only 25% of the sodium hydroxide reacting with aluminium phosphate is recovered by the Bayer process and none from iron phosphates (equation 3).
My process has the advantage that capital and operating cost of the large decomposers, evaporators and seed recycle equipment is eliminated. The relatively small amount of alkali metal carbonate produced in decomposing the alkali metal aluminate is recycled to dissolve more phosphate rock by reactions 1 and 2.
My process has the additional advantage that potassium carbonates and hydroxide can be used to produce valuable potassium phosphate. If potassium hydroxide is used to dissolve iron and aluminium phosphates the resulting potassium aluminate is not suitable for recovery of potassium hydroxide by a process analagous to the Bayer process with sodium aluminate, but potassium aluminate can be readily decomposed by carbon dioxide.
The invention will be further illustrated by the following non-limiting examples.
EXAMPLE 1
One hundred grams of Barrandite from Christmas Island was ground in hot sodium carbonate solution recycled from previous experiments and leached in agitated vessels for one hour at 70° C. This dissolved about 13% of phosphate present in the original rock.
The ground barrandite slurry was further reacted with sodium hydroxide in agitated vessels.
This sodium hydroxide was added as a 50% solution and the barrandite suspension agitated for 30 minutes at 80° C. The amount of sodium hydroxide added was calculated to be stoichiometrically equivalent to the "caustic available" phosphate present in the original barrandite. "Caustic available" phosphate is defined as total phosphorous less 0.5 times the calcium present e.g. roughly equivalent to calcium phosphate.
Residual solids, consisting largely of insoluble iron compounds and calcium phosphate, were filtered from the leach solution at 70° C. This clarified solution was then cooled to 20° C. when practically all the phosphate present crystallized as sodium orthophosphates.
The sodium orthophosphates were filtered off and the residual sodium aluminate solution reheated to 35° C. and a small amount of aluminium hydroxide added to promote subsequent precipitation. Carbon dioxide was bubbled into the solution to suspend the aluminium hydroxide and decompose the sodium aluminate to sodium carbonate and aluminium hydroxide. After three hours carbonation the aluminium hydroxide was filtered off at 35° C. and the resulting sodium carbonate solution cooled to 20° C. to crystallize out and recover sodium carbonate. The residual solution containing sodium carbonate and a small amount of sodium phosphate was recycled for leaching more barrandite.
By this technique I was able to recover over 90% of the soluble phosphate in barrandite. Of the sodium reacting to form sodium aluminate, approximately 20% of the sodium hydroxide used, over 90% of it was recovered in the form of sodium carbonate.
EXAMPLE 2
In this experiment the same technique was used as in Example 1 except that after grinding and leaching in recycled sodium carbonate, the ground barrandite slurry was heated to boiling point to drive off some of the carbon dioxide present as sodium bicarbonate. By this means the amount of sodium hydroxide used for subsequent leaching was reduced to 90% of stoichiometric.
EXAMPLE 3
In this experiment potassium carbonate and potassium hydroxide were used instead of the sodium compounds in Example 2. Because of the greater causticity of the potassium salts approximately 20% of the caustic available phosphate was solubilised during grinding and the amount of potassium hydroxide used for subsequent leach was reduced to 85% of stoichiometric. The overall effect was that no byproduct potassium carbonate was produced and the solution after aluminium hydroxide precipitation could be recycled direct to grinding.
It will be clearly understood that the invention in its general aspects is not limited to the specific details referred to hereinabove.

Claims (8)

The claims defining the invention are as follows; I claim:
1. A process for production of alkali metal phosphates from naturally occurring phosphate rock which has not been chemically treated to extract phosphates, the phosphate content of the rock being predominantly iron phosphates and aluminum phosphates, the process comprising leaching the phosphate rock with alkali metal carbonate solution to produce a leachate containing dissolved alkali metal phosphates, separating the leachate from undissolved residual solids and recovering the alkali metal phosphates from the leachate.
2. A process as in claim 1 including leaching said residual solids with alkali metal hydroxide to effect further dissolution of phosphates, and recovering alkali metal phosphates from the hydroxide leachate.
3. A process according to claim 1 in which the leaching with alkali metal carbonate solution is carried out at elevated temperature.
4. A process according to claim 3 in which the leaching with alkali metal carbonate solution is carried out under pressure at 100° to 150° C.
5. A process for production of alkali metal phosphates from naturally occurring phosphate rock containing predominantly iron phosphates and aluminum phosphates which comprises leaching the rock with alkali metal carbonate solution at 70°-100° C. to effect dissolution of phosphate from the rock, separating the leachate from undissolved residual solids, adding alkali metal hydroxide solution to the residual solids and continuing the treatment to effect further dissolution of phosphates from the rock, removing residual solids from the leachate, and cooling the leachate to precipitate phosphates therefrom.
6. A process according to claim 5, in which the solution from which the phosphates have been precipitated is carbonated with carbon dioxide to precipitate aluminum hydroxide therefrom, and the precipitated aluminum hydroxide is removed to produce a solution of alkali metal carbonate which may be recycled to the initial leaching step.
7. A process according to claim 5 in which the alkali metal carbonate is sodium carbonate.
8. A process according to claim 5 in which the alkali metal carbonate is potassium carbonate.
US06/636,601 1983-08-04 1984-08-01 Extracting soluble phosphates from naturally occurring iron and aluminium phosphates using solutions of alkali metal carbonates and hydroxides Expired - Fee Related US4609535A (en)

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CA (1) CA1249709A (en)
DE (1) DE3428735A1 (en)
FR (1) FR2550181B1 (en)
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MY (1) MY102220A (en)
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU568666B2 (en) * 1983-08-25 1988-01-07 Thomas, G. Production of phosphates from alkali-proecessed phosphate rock
US5221466A (en) * 1989-04-20 1993-06-22 Freeport-Mcmoran Resource Partners, Limited Partnership Phosphate rock benefication
US6562308B1 (en) 2000-11-15 2003-05-13 Agrium, Inc. Process for the recovery of phosphate from phosphate rock

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU568132B2 (en) * 1983-06-24 1987-12-17 Thomas, G. Alkali metal phosphates
BE1015790A3 (en) * 2003-12-24 2005-09-06 Ecophos Method phosphate strong foundations of preparation.
JP4948426B2 (en) * 2008-01-09 2012-06-06 中国電力株式会社 Strain gauge calibration system, strain gauge calibration device, and strain gauge calibration method
CN115818604B (en) * 2022-12-12 2024-07-26 湖北虹润高科新材料有限公司 Method for preparing battery-grade anhydrous ferric phosphate by reducing red mud with sulfite to extract iron solution

Citations (14)

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SU345938A1 (en) * Н. И. Волынкин, В. М. Ярыгин , М. М. Алексее Ленинградский институт киноинженеров ALL-UNION InATc "T! Fi'- GEL ^ WHECHML! ^ Hs ;;; -: O -:;: cl-
US1252318A (en) * 1917-06-07 1918-01-01 Carroll Allen Process of making acid calcium phosphates.
US1799882A (en) * 1924-03-21 1931-04-07 Firm Of Rhenania Ver Chemische Process for producing fertilizer
US1935474A (en) * 1932-05-26 1933-11-14 Bozel Maletra Prod Chimiques Preparation of alkali phosphates
US1961127A (en) * 1932-08-09 1934-06-05 Warner Chemical Company Making disodium phosphate
US2220790A (en) * 1939-02-23 1940-11-05 Monsanto Chemicals Process for the production of alkali metal phosphates
US2221356A (en) * 1937-07-15 1940-11-12 Chem Fab Budenheim Ag Manufacture of alkall phosphates
US2430863A (en) * 1941-05-05 1947-11-18 Colton Henry Seymour Processes for recovering values from calcerous and siliceous materials
GB804292A (en) * 1955-03-29 1958-11-12 Lummus Co Process for producing fertilizers and products thereof
CA606795A (en) * 1960-10-11 N. Baumann Arthur Method for preparing potassium phosphates
US4113184A (en) * 1977-09-19 1978-09-12 Cf Industries, Inc. Wet grinding method for crude phosphate rock
US4167406A (en) * 1977-03-02 1979-09-11 Kali-Chemie Aktiengesellschaft High temperature decomposition process for producing an alkali-containing calcined phosphate fertilizer
US4321244A (en) * 1979-09-07 1982-03-23 Groupement Franco-Senagalais D'etudes Et De Recherches Industrielles Process for the treatment of a calcium aluminophosphate
US4374817A (en) * 1981-08-21 1983-02-22 Fmc Corporation Formulation of phosphate rock slurries

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DE532860C (en) * 1929-09-11 1931-09-04 I G Farbenindustrie Akt Ges Production of alkali phosphate and hydrogen
FR754294A (en) * 1933-08-11 1933-11-02
DE622229C (en) * 1934-01-14 1935-11-22 Chemische Werke Vorm H & E Alb Production of trinastrum phosphate
FR1198093A (en) * 1958-04-14 1959-12-04 Process for preparing alumina and trisodium phosphate or tripotassium phosphate
FR2390380A1 (en) * 1977-05-09 1978-12-08 Douglas & Lomason Co Recovering phosphates from aluminium bright dip operations - by reaction with sodium hydroxide to form useful trisodium phosphate
AU568132B2 (en) * 1983-06-24 1987-12-17 Thomas, G. Alkali metal phosphates
AU568666B2 (en) * 1983-08-25 1988-01-07 Thomas, G. Production of phosphates from alkali-proecessed phosphate rock

Patent Citations (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA606795A (en) * 1960-10-11 N. Baumann Arthur Method for preparing potassium phosphates
SU345938A1 (en) * Н. И. Волынкин, В. М. Ярыгин , М. М. Алексее Ленинградский институт киноинженеров ALL-UNION InATc "T! Fi'- GEL ^ WHECHML! ^ Hs ;;; -: O -:;: cl-
US1252318A (en) * 1917-06-07 1918-01-01 Carroll Allen Process of making acid calcium phosphates.
US1799882A (en) * 1924-03-21 1931-04-07 Firm Of Rhenania Ver Chemische Process for producing fertilizer
US1935474A (en) * 1932-05-26 1933-11-14 Bozel Maletra Prod Chimiques Preparation of alkali phosphates
US1961127A (en) * 1932-08-09 1934-06-05 Warner Chemical Company Making disodium phosphate
US2221356A (en) * 1937-07-15 1940-11-12 Chem Fab Budenheim Ag Manufacture of alkall phosphates
US2220790A (en) * 1939-02-23 1940-11-05 Monsanto Chemicals Process for the production of alkali metal phosphates
US2430863A (en) * 1941-05-05 1947-11-18 Colton Henry Seymour Processes for recovering values from calcerous and siliceous materials
GB804292A (en) * 1955-03-29 1958-11-12 Lummus Co Process for producing fertilizers and products thereof
US4167406A (en) * 1977-03-02 1979-09-11 Kali-Chemie Aktiengesellschaft High temperature decomposition process for producing an alkali-containing calcined phosphate fertilizer
US4113184A (en) * 1977-09-19 1978-09-12 Cf Industries, Inc. Wet grinding method for crude phosphate rock
US4321244A (en) * 1979-09-07 1982-03-23 Groupement Franco-Senagalais D'etudes Et De Recherches Industrielles Process for the treatment of a calcium aluminophosphate
US4374817A (en) * 1981-08-21 1983-02-22 Fmc Corporation Formulation of phosphate rock slurries

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU568666B2 (en) * 1983-08-25 1988-01-07 Thomas, G. Production of phosphates from alkali-proecessed phosphate rock
US5221466A (en) * 1989-04-20 1993-06-22 Freeport-Mcmoran Resource Partners, Limited Partnership Phosphate rock benefication
US6562308B1 (en) 2000-11-15 2003-05-13 Agrium, Inc. Process for the recovery of phosphate from phosphate rock

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BR8403903A (en) 1985-07-09
GB2144726A (en) 1985-03-13
GB2144726B (en) 1987-02-18
GB8419169D0 (en) 1984-08-30
CA1249709A (en) 1989-02-07
OA07920A (en) 1986-11-20
JPS6054908A (en) 1985-03-29
AU571549B2 (en) 1988-04-21
NZ208986A (en) 1987-06-30
DE3428735A1 (en) 1985-02-21
FR2550181A1 (en) 1985-02-08
MY102220A (en) 1992-05-15
AU3093284A (en) 1985-02-07
FR2550181B1 (en) 1988-02-19

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